1. Field of the Invention
The present invention relates to a distributed input-distributed output wireless communication system using space-time coding techniques. More particularly, the present invention relates to a method for approximating Symbol Error Rate (SER) performance for an Orthogonal Space Time Block Code (OSTBC) equipped with multiple transmission Distributed Antennas.
2. Description of the Related Art
Relatively recently-developed techniques for wireless communication include a spatial multiplexing technique and a space-time coding technique. One specific type of space-time coding is referred to as “MIMO” for Multiple Input Multiple Output. The MIMO technique typically uses a plurality of antennas in receiving and transmitting signals, so that multiple independent radio waves can be transmitted at the same time within the same frequency.
In general the MIMO technique is based on use of spatially separated antennas by generating parallel space data streams within a common frequency bandwidth. Even if individual signals are to be transmitted within the same frequency, the radio waves are transmitted such that the signals can be divided and demodulated in a receiver, so as to generate a plurality of communication channels which are statistically independent (i.e. effectively divided). Therefore, in contrast to a standard wireless communication system prohibiting multiple paths (i.e. a plurality of signals with the same frequency, which are delayed in time and have various amplitudes and phases), the MIMO technique can utilize multiple path signals having nearly no correlation (or having weak correlation), so as to accomplish an improved signal-to-noise ratio (SNR) and a larger throughput within an appropriate frequency bandwidth.
In one specific application of a MIMO technique, a theoretical result provided by references [1] and [2] presented below has indicated that a Distributed Antenna (DA) can be more advantageous than a co-located MIMO (C-MIMO) channel, in an aspect of capacity. However, research on a method for sufficiently exploiting the benefits of the capabilities of distributed antennas has not been thoroughly conducted. To this end, a concept of the Distributed Wireless Communication System (DWCS) was proposed by reference [3] presented below, and the system is expected to greatly increase system capacity because of the ability to manage transmission signals together with reception signals.
The OSTBC among various space-time codes (refers to reference [4]) is very attractive for real system arrangement on account of simple coding and decoding schemes. In future wireless communication systems, the bottle neck phenomenon may occur in transmitting downlink data, and thus an optimal downlink OSTBC design based on Channel State Information (CSI) estimation of a specific transmitter will be required to reduce or prevent such a bottle neck phenomenon.
FIG. 1 is a schematic block diagram illustrating a conventional system for OSTBC transmission through a co-located MIMO channel. Referring to FIG. 1, data symbols to be transmitted from a transmission side (i.e. a base station) are modulated by a designated modulation scheme and are input to a space-time encoder 100 for a space-time encoding, and then the resulting symbols are transmitted to a reception side 120 (i.e. a mobile terminal) through multiple co-located transmitting antennas 110. In this case, the reception side 120 has m reception antennas to receive the transmissions from the transmitting antennas.
In an OSTBC scheme through a distributed antenna, there is still no simple and exact expression for an SER. Therefore, it is very complicated to express the SER of an OSTBC transmitted through a distributed antenna, and it is thus difficult to calculate the SER. Therefore, in order to implement an actual system, a method for approximating SER in a simple and effective manner is required.
Moreover, the Chernoff upper bound of an SER is widely used for its performance analysis. However, this bound is not generally coherent, so it is difficult to directly predict the SER performance based on the Chernoff bound. Thus, there is a need in the art to provide a method for approximating an optimal.